it would be better for me if the file attachment (non images) were shown, and then when guests try to click a popup window instructing them that they need to sign up + register to gain access to the file attachments.. this would be really great

It might partly depend on what type of files the attachments will be, what type are they (documents, pictures, music, etc)?

hard to find driver files, text documentation etc in this case

Don't think the market would be there for hard to find drivers when sites like driverguide.com exist and have them for free. What sort of stuff do you mean with "text documentation"? Have you googled to see if any other site has the same stuff for free without signing-up and logging-in?